Connective tissues proper
- are marked by a high content of intercellular substance where fibers make up a considerable volume (these tissues are also called fibrous tissues)
- may have a varied amount of ground (amorphous) substance
Connective tissue proper types (loose and dense tissues) differ by features of intercellular substance arrangement
Loose connective tissue
- the intercellular substance is marked by a prevalence of amorphous component with a rather low fiber content
- collagen, elastic, and reticular fibers are not ordered in the intercellular substance
- the tissue contains interacting cells differing in their functions and origin:
- derivatives of stromal stem cells in the red bone marrow: various types of fibroblasts, adventitial cells, adipose cells
- derivatives of hematopoietic stem cells in the red bone marrow: macrophages, mast cells, granulocytes and agranulocytes, plasma cells
- derivatives of cells from the neural crest: melanocytes
- this is the most common type of connective tissues. It constitutes the stroma of many organs (layers between lobules, membranes, and layers); it envelops blood vessels and nerves, composes the skin and mucous membranes
Dense irregular connective tissue
- its intercellular substance contains collagen and elastic fibers predominantly; there is little ground substance
- the collagen fibers are arranged in bundles that are not ordered. These bundles interlace forming a 3D network
- fibroblasts and fibrocytes are the most common cells, macrophages are not so common, as well as mast cells and white blood cells
- the tissue is found in the dermis, capsules of parenchymatous organs, perichondrium, and periosteum
Dense regular connective tissue
- its intercellular substance is represented by collagen fiber bundles that are parallel to one another
- there are elastic fibers and a little ground substance between the collagen fiber bundles
- cells are not abundant, most of them are fibrocytes
- this is the main tissue in tendons, ligaments, and aponeuroses